Preheater for arc furnaces

ABSTRACT

To provide a pre-heating apparatus capable of improving the installation reliability of a raw material holding gate of a pre-heating apparatus, reducing an installation cost and reducing melting electric power energy without deteriorating an operation environment while improving the pre-heating effect on raw materials by an exhaust gas, a shaft equipped with a raw material charging portion and an exhaust gas outlet at the top thereof and with a raw material holding gate at the bottom thereof is disposed in the proximity of an arc furnace, a gap is defined between the lower end portion of the shaft and the holding gate, and an outer cylinder connecting with an exhaust gas duct of the arc furnace is disposed around the outer periphery of the gap.

This application is a National Phase under 35 U.S.C. §371 ofPCT/JP96/01003 filed Apr. 11, 1996.

TECHNICAL FIELD

This invention relates to a pre-heating apparatus for an arc furnacewhich is used for melting metallic material and for refining moltenmetals. Specifically, the invention relates to a pre-heating apparatuscapable of preventing a non-uniform flow of an exhaust gas inside ashaft, relieving a thermal load on a gate for holding a raw material andreducing an installation cost.

BACKGROUND ART

Arc furnaces for refining include a D.C. arc furnace which causes acurrent to flow between an electrode disposed above metallic materialscharged into the furnace and an electrode fitted to a furnace bottom ora furnace wall such as a side wall and which effects melting of themetallic materials and refines a molten metal, and an A.C. arc furnacewhich causes a current to flow through three electrodes disposed abovethe molten metal charged into the furnace, and effects melting of themetallic materials and refining of the molten metal. Exhaust gasutilization systems in the arc furnaces of these kinds generally haveconstructions wherein a pre-heating vessel is disposed between the arcfurnace and dust collecting equipment, a bucket of the metallicmaterials is inserted into this pre-heating vessel and the metallicmaterials are pre-heated by an exhaust gas.

However, the exhaust gas duct between the arc furnace and thepre-heating vessel has a water-cooling structure because a hightemperature gas generated by the arc furnace flows through this duct,and the temperature of the exhaust gas reaching the pre-heating vesseldrops to an extent corresponding to the temperature drop due towater-cooling. Therefore, the retained heat of the exhaust gas cannot beefficiently utilized for pre-heating the metallic materials, and this isa critical problem from the aspect of heat efficiency. Further, thewhite smoke and the offensive odor that are generated when thepre-heated metallic materials are conveyed in the bucket to the arcfurnace are also a critical problem from the aspect of the operatingenvironment.

Therefore, various proposals have been made so far in order toefficiently utilize the heat of the exhaust gas for pre-heating the rawmaterials and to charge the pre-heated raw materials into the arcfurnace without conveying them from the pre-heating vessel to the arcfurnace. Japanese Unexamined Patent Publication (Kokai) No. 3-505625,for example, describes an arc furnace which pre-heats the raw materialsin a pre-heating zone formed by a shaft disposed on a furnace cover anda part of a furnace body and lets the pre-heated raw materials, whichare stored in the shaft, drop naturally.

In this case, however, after the raw materials stored in the shaftdisposed on the furnace cover naturally drop and are then molten, or inother words, at the so-called "refining stage", the raw materials nolonger exist inside the shaft, and are not pre-heated by the heat of theexhaust gas any more. Therefore, the problem of heat efficiency wasstill unsolved.

To solve this problem, Japanese Unexamined Patent Publication (Kokai)No. 5-500263, for example, proposes a method which disposes two sets ofarc furnaces, introduces the exhaust gas into the other of the arcfurnaces, which stores the raw materials inside the shaft and is in astand-by state, so as to pre-heat the raw materials after the rawmaterials stored in one of the arc furnaces naturally drop and aremolten by electric power supplied to this arc furnace, and pre-heats theraw materials by the other arc furnace so as to improve heat efficiency.

Japanese Unexamined Patent Publication (Kokai) No. 4-309789 proposes amethod which forms the pre-heating zone in only the shaft, disposes araw material holding gate inside the shaft, makes it possible to alwaysstore the raw materials inside the shaft and thus utilizes the heat ofthe exhaust gas at the refining stage.

By the way, a major portion of the energy for melting the metallicmaterials in the arc furnace is provided by electrical energy. When theenergy efficiency for melting the metallic materials is taken intoconsideration, it is desirable to position the arc as the energy sourceas close as possible to the center portion of the furnace body, that is,to dispose the upper electrode to bring the charging portion of themetallic materials to be molten as close as possible to the centerportion of the furnace body and to generate the arc from the upperelectrode at the center of the metallic materials so as to uniformlymelt them throughout the periphery.

This proposal exploits fully the great advantage of the D.C. arc furnacein that only one upper electrode is needed and the energy utilizationefficiency is higher than the A.C. arc furnace which requires threeupper electrodes. This advantage quite naturally holds true of the casewhere the metallic materials, as the object of melting, are pre-heated.

However, in the prior art proposals of Japanese Unexamined PatentPublications (Kokai) Nos. 3-505625, 5-500263 and 4-309789 describedabove, the shaft is disposed on the side wall portion of the furnacebody and the pre-heated raw materials are therefore charged to only theside wall portion of the furnace body. In other words, the portion ofthe furnace body opposite to this side wall portion to which the rawmaterials are not charged is always heated uselessly by the arc heat andis not used for melting the raw materials, thereby inviting the drop ofenergy utilization efficiency. Since the raw materials are charged onlyto the portion of the furnace away from the upper electrode, the meltingspeed becomes lower than the case where melting is carried out bydisposing the upper electrode above the center portion of the rawmaterials, and energy utilization efficiency drops.

To solve this problem, it may be conceivable to employ a method whichcharges the raw materials while the furnace cover and the shaft aremoved so that the shaft comes to the center portion of the furnace body.In this case, the upper part of the furnace body is opened with themovement of the furnace cover in the furnace cover shape according tothe prior art, and when the raw materials inside the shaft are chargedinto the furnace, a gas containing high temperature dust is blasted outfrom the upper portion of the furnace body and remarkably deterioratesthe operation environment.

In an arc furnace wherein a shaft for pre-heating raw materials isdisposed on a furnace cover, and this shaft and an upper electrode arepositioned at the center of the furnace cover and capable of moving upand down are integrally disposed, Japanese Patent Application No.6-144079 filed previously by the inventors of the present invention tosolve the problem described above employs the construction wherein thefurnace cover is movably constituted and the furnace cover covers theupper portion of the furnace body even at the time of movement.

DISCLOSURE OF THE INVENTION

Even in the improved system described above, there remains the followingproblem to be solved. The system which holds the raw materials insidethe shaft disposed on the furnace cover and pre-heats them is anadvantageous system from the aspect of heat recovery because it candirectly utilize the high temperature exhaust gas from the arc furnace.However, the holding gate of the raw materials disposed inside the shaftreceives the drop impact load at the time of charging of the rawmaterials into the shaft, and must pass the high temperature exhaust gasfrom the arc furnace while receiving the load of the raw materialsduring pre-heating.

Therefore, openings for gas passage such as slit-like grooves arenecessary, and since the entire surface of the holding gate exposedinside the shaft is exposed to the high temperature exhaust gas, it musthave various performance features such as extremely high strength,heat-resistance and high wear resistance in combination. Accordingly,problems are yet left in the aspects of reliability of equipment and theinstallation cost.

To cope with this problem, it may be possible to employ a method whichdisposes the shaft in the proximity of the arc furnace, disposes the rawmaterial charging portion and an exhaust gas outlet at the top of theshaft and the raw material holding gate capable of being sealed to thebottom of the shaft, introduces the exhaust gas from the arc furnace tothe side wall portion of the shaft through an exhaust gas duct tothereby eliminate the necessity for the passage of the exhaust gasthrough the raw material holding gate portion, and thus reduces thethermal load to the holding gate. In this case, however, because theintroduction direction of the exhaust gas into the shaft becomesunidirectional, it happens that a non-uniform flow of the gas occursinside the shaft, the drop in pre-heating efficiency occurs.

It is therefore an object of the present invention to provide apre-heating apparatus of an arc furnace capable of improving equipmentreliability of a raw material holding gate, reducing an installationcost, and reducing electric power energy requirements for melting thepre-heated raw materials while improving pre-heating efficiency of theraw materials by an exhaust gas but without deteriorating an operationenvironment.

The present invention provides a pre-heating apparatus of an arc furnacewhich includes a shaft disposed in the proximity to an arc furnacehaving an exhaust gas duct for exhausting a furnace gas on a furnacebody or a furnace cover, and having a raw material charging portion andan exhaust gas outlet at the top thereof and a holding gate for holdingthe raw materials charged at the bottom thereof, and which pre-heats theraw materials charged into the shaft by an exhaust gas generated by thearc furnace so as to effectively utilize retention heat of the exhaustgas.

The gists of the pre-heating apparatus of an arc furnace according tothe present invention reside in the following points.

(1) A pre-heating apparatus for an arc furnace characterized in that ashaft is provided to a furnace body or a furnace cover in the proximityof an arc furnace having an exhaust gas duct for exhausting a furnacegas, a raw material charging portion and an exhaust gas outlet aredisposed at the top of the shaft, a holding gate is disposed in such amanner as to keep a predetermined gap with the lower end portion of aside wall of the shaft, an outer cylinder connecting with an exhaust gasduct from the arc furnace through a connecting duct is disposed roundthe lower portion of the side wall of the shaft, and a moving devicecapable of moving in a horizontal direction is disposed so as to set thefurnace body or the shaft at a predetermined operating position.

(2) A pre-heating apparatus of an arc furnace according to item (1),wherein a hood is disposed at a lower portion of the shaft, and the hoodis capable of covering an opening of the upper surface of the furnacebody when raw materials are charged into the furnace.

(3) A pre-heating apparatus of an arc furnace according to item (1),wherein dust collecting ducts capable of communicating with the exhaustgas outlet at the top of the shaft are disposed at the position at whichthe raw materials are pre-heated inside the shaft and at the position atwhich the raw materials are charged into the furnace, respectively, inthe positional relationship between the furnace body of the arc furnaceand the shaft.

(4) A pre-heating apparatus for an arc furnace according to item (1),wherein the furnace cover and an upper electrode are allowed to move ina horizontal direction while keeping a predetermined positionalrelationship with the shaft when the furnace body or the shaft is movedin the horizontal direction.

(5) A pre-heating apparatus for an arc furnace according to item (4),wherein a driving device is provided so as to move the upper electrodeand an elevating device for the electrode in the horizontal direction,detectors for detecting displacement such as extension and contractionare provided to driving devices for tilting the furnace body of the arcfurnace and for moving the upper electrode in the horizontal direction,respectively, and a computer is further disposed so as to calculatedisplacement of an upper electrode through-hole disposed in the furnacecover from the displacement of the driving device for tilting thefurnace body of the arc furnace and to calculate further thedisplacement of the driving device for moving the upper electrode in thehorizontal direction on the basis of the displacement of the upperelectrode through-hole.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is an overall longitudinal sectional view of an arc furnace and apre-heating apparatus in an embodiment according to the presentinvention.

FIG. 2 is an overall longitudinal sectional view when raw materialsinside the pre-heating apparatus of the arc furnace are charged into thefurnace in an embodiment according to the present invention.

FIG. 3 is a view taken on a line A--A of FIG. 1.

FIG. 4 is an explanatory view representing the positional relationshipbetween a furnace cover and an upper electrode when a furnace body istilted during the operation of the arc furnace in the embodimentaccording to the present invention.

BEST MODE FOR CARRYING OUT THE INVENTION

The exhaust gas duct for exhausting the furnace gas is disposed on thefurnace body or the furnace cover of the arc furnace and is connectedthrough the connecting duct to the lower portion of the shaft equippedwith the raw material charging portion and the exhaust gas outlet at thetop thereof and the holding gate for holding the charged raw materialsat the bottom thereof.

In other words, in the pre-heating apparatus of the arc furnace of thetype wherein the exhaust gas generated in the arc furnace is introducedthrough the exhaust gas duct and the connecting duct into the shaft soas to pre-heat the raw materials charged into the shaft and the furnacebody or the shaft is allowed to move in the horizontal direction so asto charge the pre-heated raw materials into the furnace body by openingthe holding gate, the shaft is shaped in such a manner that the lowerend portion of its side wall defines a gap with the holding gate, theouter cylinder for preventing intrusion of external air is disposedround the lower portion of the side wall, the connecting duct forintroducing the exhaust gas generated in the arc furnace is connected tothis outer cylinder, and the exhaust gas is introduced into the shaftthrough the gap between the outer cylinder and the side wall of theshaft.

Accordingly, the gap between the outer cylinder and the shaft side wallhas the function of a header pipe, and the exhaust gas introduced fromthe arc furnace is uniformly distributed in the peripheral direction atthe gap portion between the shaft side wall lower portion and the outercylinder, and the exhaust gas introduced into the shaft is also madeuniform in the peripheral direction and is allowed to flow. Since anon-uniform flow of the exhaust gas is thus eliminated inside the shaft,the pre-heating efficiency of the raw materials can be improved, andeffective utilization of the retained heat of the exhaust gas can beaccomplished.

Further, the exhaust gas of the arc furnace is introduced from above theraw material holding gate disposed at the bottom of the shaft, risesinside the shaft and is exhausted from the exhaust gas outlet disposedat the top of the shaft. Therefore, the passage of the exhaust gas inthe vertical direction while the raw material holding gate is interposeddoes not occur, and it is only the upper surface side of the rawmaterial holding gate that is affected by the high temperature exhaustgas, while the lower surface side is in contact with the atmosphere. Inconsequence, the counter-measure structure for the holding gate withrespect to heat resistance becomes extremely simple, and an improvementin equipment reliability and a reduction of the equipment cost can beaccomplished.

Further, the hood for covering the opening of the upper surface of thefurnace body is disposed at the lower portion of the shaft at which theraw materials are charged into the furnace, and the dust collecting ductcapable of communicating with the exhaust gas outlet at the top of theshaft is disposed at that position so as to remove the exhaust gas.Accordingly, when the holding gate is opened so as to charge the rawmaterials into the furnace, the hood collects the high temperature gascontaining large quantities of dust generated from the furnace.Thereafter, the exhaust gas passes through the shaft and is removed fromthe exhaust gas outlet at the top of the shaft. In this way, theresulting gas from the arc furnace at the time of charging of the rawmaterials can be efficiently collected.

Because the furnace or the shaft can move in the horizontal direction,the upper electrode can be situated at the center of the furnace bodyduring the melting operation of the arc furnace, and the raw materialscan be charged to the center portion of the furnace body when they arecharged into the furnace. Therefore, the energy utilization efficiencyof the arc can be improved.

In the melting and refining operation by the arc furnace, there is thecase where the furnace body is tilted while the furnace cover is put onthe furnace body and power is applied. In this case, in the system wherethe upper electrode moves in the horizontal direction while keeping apredetermined positional relationship with the shaft, there may be themethod which enlarges the electrode through-hole to match the tiltingrange of the furnace body. In this case, however, the intrusion quantityof external air through this electrode through-hole increases, and adrop in the heat efficiency of the arc furnace undesirably develops.

Therefore, the driving device for moving the upper electrode and theelevation device of the electrode in the horizontal direction isdisposed and furthermore, the displacement detectors for the drivingdevice for tilting the furnace body of the arc furnace and the drivingdevice for the upper electrode in the horizontal direction are disposed,respectively. A computer is further disposed for these displacementdetectors.

When the furnace body is tilted while the furnace cover is put on thefurnace body, the displacement quantity of the driving device fortilting the furnace body such as extension and contraction of ahydraulic cylinder is detected, the displacement quantity of the upperelectrode through-hole disposed in the furnace cover is computed on thebasis of the displacement quantity so detected, and the upper electrodeis moved in the horizontal direction in such a manner as to follow upthe displacement quantity. In this way, enlargement of the electrodethrough-hole can be prevented, intrusion of external air into thefurnace can be reduced, and the drop of heat efficiency of the arcfurnace can be prevented.

Next, the embodiment of the invention will be explained with referenceto the attached drawings.

EXAMPLE

FIG. 1 is an overall longitudinal sectional view of an arc furnaceaccording to the present invention, and FIG. 2 is an overalllongitudinal sectional view when raw material inside a shaft of the arcfurnace according to the present invention are charged into the furnace.FIG. 3 is a view taken on a line A--A in FIG. 1, and FIG. 4 is anexplanatory view showing the positional relationship between a furnacecover and an upper electrode when a furnace body is tilted during theoperation of the arc furnace.

A furnace cover 2 having an exhaust duct 4 for exhausting a furnace gasis disposed at the upper part of a furnace body 1, and an upperelectrode 3 is so disposed as to penetrate through the furnace cover 2.A driving device 15 is provided to the furnace body 1 so that thefurnace body can be tilted, whenever necessary, during the meltingoperation.

A shaft 5 is disposed in the proximity of the furnace body 1. A rawmaterial charging portion 10 and an exhaust gas outlet 11 are disposedat the top of this shaft 5 while a gate 7 for holding the raw material20 charged into the shaft is disposed at the bottom portion.

Dust collecting ducts 16 and 17 are disposed at the position at whichthe raw materials 20 are pre-heated inside the shaft 5 and at theposition at which the raw materials 20 are charged into the furnace,respectively. Dampers 18 and 19 are provided to these dust collectingducts 16 and 17, respectively, and these dust collecting ducts 16 and 17are further communicated with dust collecting equipment (not shown inthe drawing).

The sectional shape 5 of the shaft 5 may be either circular or square,and the shaft 5 is preferably tapered downward so as to prevent cloggingof the raw materials 20 inside the shaft 5.

A predetermined gap 9 is defined between the lower end portion of theshaft 5 and the holding gate 7, and is preferably disposed around theentire periphery of the lower end portion of the shaft. Further, anouter cylinder 6 connected to the exhaust gas duct 4 described abovethrough a connecting duct 8 is disposed around the outer periphery ofthe shaft.

A hood 12 is disposed at the lower portion of the shaft 5 in such amanner as to cover an opening of the upper surface of the furnace body 1when the raw materials 20 are charged into the furnace body 1, and thishood 12 is so shaped as to accommodate therein the raw material holdinggate 7.

Moreover, in the embodiment, the furnace cover 2, the upper electrode 3and the shaft 5 are supported by a moving device 13 so that the furnacecover 2 and the upper electrode 3 can move in the horizontal directionwhile keeping the positional relationship with the shaft 5 in apredetermined relationship.

Moreover, as another embodiment, the furnace cover 2 and the upperelectrode 3 may be moved by a different driving system, e.g. a drivingdevice for turning, and the shaft 5 may be supported by the movingdevice 13 so that the shaft 5 can move in the horizontal direction.

The operation of the apparatus having the construction described abovewill be explained in further detail.

A high temperature exhaust gas generated from the furnace body 1 duringthe melting operation is guided into the outer cylinder 6 disposed atthe lower portion of the shaft 5 through the exhaust gas duct 4 and theconnecting duct 8. The exhaust gas is then guided into the shaft 5through the gap 9 between the lower portion of the shaft 5 and theholding gate 7.

In this instance, since the gap 9 is formed throughout the entireperiphery of the lower portion of the shaft 5, gas is introduceduniformly into the shaft 5 in the circumferential direction, and anon-uniform flow of the gas can be eliminated inside the shaft 5.Therefore, the raw materials 20 inside the shaft can be efficientlypre-heated. Because the high temperature exhaust gas flows only on theupper surface side of the holding gate 7 disposed at the bottom of theshaft 5 in this case, the thermal load to the holding gate 7 is smalland the reliability of the equipment can be drastically improved.

The gas after pre-heating is exhausted through the exhaust gas outlet 11disposed at the top of the shaft, is introduced into the dust collectingequipment, not shown, and is thereafter exhausted into air.

When the raw materials are changed into the furnace, the furnace cover 2and the upper electrode 3 are moved up, and the furnace cover 2, theupper electrode 3 and the shaft 5 are moved, integrally with oneanother, by the moving device 13. After the shaft 5 stops at the centralposition of the furnace body 1, the holding gate 7 is opened and the rawmaterials 20 are charged into the furnace.

The raw materials 21 so charged into the furnace are distributed into amountain shape having the top thereof at the center of the shaft on thetransverse sectional plane. In this instance, the opening on the uppersurface of the furnace body 1 is covered by the hood 12 and furthermore,the exhaust gas outlet 11 at the top of the shaft 5 is connected to thedust collecting duct 17. Therefore, the high temperature exhaust gas,which is generated at the time of charging of the raw materials andcontains large quantities of dust, can be efficiently collected byopening the damper 19 disposed on the dust collecting duct 17, anddeterioration of the operation environment can be prevented.

After the raw materials are charged into the furnace, the moving device13 moves to the pre-heating position of the raw materials 20 inside theshaft, the upper electrode 3 is lowered and generates an arc at thecenter portion of the raw materials and melting starts.

As can be clearly understood from the explanation given above, theposition of the upper electrode most preferred from the aspect ofmelting efficiency and the charging position of the raw materials, ormore concretely, the position of the upper electrode 3 and the chargingposition of the raw materials 20, can be situated at the center of thefurnace body 1.

Next, the explanation will be given on a horizontal movement controlmechanism of the upper electrode when the furnace body 1 is tilted whilethe furnace cover 2 is placed on the furnace body 1.

The furnace body 1 includes a driving device 15 for tilting and tiltswith the center of tilting 26 as the center. The upper electrode 3 andan elevating device (not shown) of this electrode include a drivingdevice 27 for horizontal movement, and each of these driving devicesincludes a displacement detector 28, 29.

An encoder, or the like, can be used for these detectors. Further, acomputer 30 for an arithmetic operation of the displacement is provided.Next, the method of using these means will be explained.

The length displacement quantity between the displacement referencelength 22 of the driving device 15 for tilting at the erect position ofthe furnace body 1 and the displacement length 23 of the driving device15 at the tilted position of the furnace body 1, the relationshipbetween this length displacement quantity and the tilted displacementangle 24 of the furnace body, and the relationship between the tilteddisplacement angle 24 and the length displacement quantity 25 of theupper electrode through-hole in the horizontal direction are determinedby their dimensions, respectively, and these relational formulas arestored in advance in the computer 30.

The computer calculates the central position of the upper electrodethrough-hole of the furnace cover 2 by using the displacement detectionvalue of the driving device 15 for tilting, and controls the drivingdevice 27 for horizontal movement so that the center of the upperelectrode is coincident with the central position so calculated. In thisway, mechanical interference between the upper electrode 3 and the upperelectrode through-hole of the furnace cover 2 can be prevented.Furthermore, because the open area of the electrode through-hole can bekept small, the intrusion of external air into the furnace can bereduced to minimum.

The explanation given above represents the case where the shaft 5disposed in the proximity of the arc furnace is moved in the horizontaldirection, but the present invention can be of course applied similarlyto the system where the furnace body is moved in the horizontaldirection.

INDUSTRIAL APPLICABILITY

As explained above, according to the pre-heating apparatus for the arcfurnace of the present invention, the thermal load on the gate forholding the raw materials can be reduced. Therefore, the equipmentreliability of the holding gate can be drastically improved, and theinstallation cost of the holding gate can be reduced.

Because the header space and the predetermined gap are secured at thelower portion of the shaft and because the exhaust gas of the arcfurnace can be thus introduced uniformly into the shaft, a non-uniformflow of the gas can be restricted, and the pre-heating efficiency of theraw materials by the exhaust gas can be improved. Because the upperelectrode and the raw material charging position can be positioned atthe center of the furnace body, melting efficiency can be improved.

Because the exhaust gas generated at the time of charging of the rawmaterials into the furnace can be efficiently collected, the operationenvironment can be drastically improved. Because the size of the upperelectrode through-hole of the furnace cover can be reduced to minimum,the intrusion quantity of external air into the furnace can berestricted to minimum and the drop of heat efficiency of the arc furnacecan be prevented.

As described above, the present invention can make a great contributionin improving productivity by an improvement in melting efficiency,reducing melting energy, improving equipment reliability, reducing theinstallation cost, improving the operation environment, and the like.

We claim:
 1. A pre-heating apparatus for an arc furnace characterized inthat a shaft is provided in proximity to a furnace body and a furnacecover of an arc furnace having an exhaust gas duct for exhausting afurnace gas, a material charging port and an exhaust gas outlet aredisposed at the top of said shaft, a holding gate is disposed in such amanner as to keep a predetermined gap with the lower end portion of aside wall of said shaft, an outer cylinder connecting with said exhaustgas duct from said arc furnace through a connecting duct is disposedaround the gap and the lower end portion of the side wall of said shaft,a moving device capable of moving in a horizontal direction is disposedso as to set said shaft at a predetermined operating position, andfurther a hood is disposed at a lower portion of said shaft, and saidhood is capable of covering an opening of the upper surface of saidfurnace body when raw materials are charged into the furnace, andfurther dust collecting ducts capable of communicating with said exhaustgas outlet at the top of said shaft are disposed at the position atwhich said raw materials are pre-heated in side said shaft and at theposition at which said raw materials are charged into said furnace inthe positional relationship between said furnace body of said arcfurnace and said shaft.
 2. A pre-heating apparatus for an arc furnaceaccording to claim 1, wherein said furnace cover and an upper electrodeare allowed to move in a horizontal direction while keeping apredetermined positional relationship with said shaft when said shaft ismoved in the horizontal direction.
 3. A pre-heating apparatus for an arcfurnace according to claim 2 further comprising:a horizontal drivingdevice for moving said upper electrode in the horizontal direction, saidupper electrode being disposed in a through-hole located in said furnacecover; an elevating device for elevating said electrode; a tiltingdevice for tilting said furnace body of said arc furnace; a firstdetector device for detecting horizontal movement of said electrode andproviding a responsive signal; a second detector device for detectingtilting of said furnace body and providing a responsive signal; acomputer for receiving said responsive signal from said first detectordevice and said second detector device and controlling said horizontaldriving device.